Add ability to log last 2 digits of dialed numbers in userdebug builds.

Filers of bugs often refer to specific phone numbers.  Bug reports by
default obscure dialed phone numbers from the Telecom logs.  This makes it
difficult to relate events in the bug report to what the bug filer refers
to.

To ease this, in userdebug builds we will now leave the last 2 digits of
dialed phone numbers un-obfuscated.  User builds will remain obfuscated.

Test: Added unit tests to cover this case.
Bug: 78457192
Change-Id: Ifbd7cbba0869d01a516d7ebd8413df2a9981de0e